Our body movements always convey something about us to other people. The body "speaks" whether we are sitting or standing, talking or just listening. On a blind date, how the two individuals position themselves tells a great deal about how the evening will unfold: Is she leaning in to him or away? Is his smile genuine or forced?

The same is true of gestures. Almost always involuntary, they tip us off to love, hate, humility and deceit. Yet for years, scientists spent surprisingly little time studying them, because the researchers presumed that hand and arm movements were mere by-products of verbal communication. That view changed during the 1990s, in part because of the influential work of psycholinguist David McNeill at the University of Chicago. For him, gestures are "windows into thought processes." McNeills work, and numerous studies since then, has shown that the body can underscore, undermine or even contradict what a person says. Experts increasingly agree that gestures and speech spring from a common cognitive process to become inextricably interwoven. Understanding the relationship is crucial to understanding how people communicate overall.